The present invention relates to a method and an apparatus for removing a photoresist on a semiconductor wafer.
In a photolithography process which is one step in a semiconductor device fabricating process, a photoresist is generally used as a mask for patterning. A film of this photoresist is removed when a patterning for a semiconductor device is completed. For a removing treatment of the photoresist film, it is a conventional practice to use a sulfuric-acid hydrogen-peroxide mixture (abbreviated to xe2x80x9cSPMxe2x80x9d hereinafter) which is heated to a temperature of not less than 100 degrees Celsius, or alternatively to use an organic solvent.
Since the removing treatment of the photoresist film using the SPM is carried out at a high temperature of not less than 100 degrees Celsius, the SPM is used after the SPM is ordinarily heated in a treating bath formed of quartz. Therefore, the amount of chemicals used becomes vary large, and in addition, the amount of the used treating liquid to be wasted correspondingly becomes voluminous.
Furthermore, in order to maintain the SPM at a high temperature in the treating bath, a load applied to a processing machine is large, and therefore, a maintenance for the processing machine must frequently be carried out. This is a disadvantage.
In the removing treatment of the photoresist film using the organic solvent, a similar problem is encountered. In particular, since the organic solvent is easy to volatilize, it is necessary to elevate the degree of sealing in the processing machine in order to prevent leak and diffusion of the organic solvent into ambiance of the processing machine. In addition, a severe management is required in a method for treating the used treating liquid (waste liquid)
In place of the SPM and the organic solvent which have the above mentioned various problems such as the load to the processing machine and the waste liquid treatment, attention is focused onto an ozone-dissolved water (ozonated water). Ozone has a high oxidative power, and the waste water has a short natural decomposition time. In addition, it is not necessary to carry out a special waste treatment. Since the ozone-dissolved water has the above mentioned various advantages, the ozone-dissolved water can be relatively easily applied into a semiconductor fabricating line.
For example, Japanese Patent Application Pre-examination Publication Nos. JP-A-01-233729, JP-A-06-275515 and JP-A-09-501017 disclose a method and an apparatus for removing the photoresist by using the ozone-dissolved water. JP-A-09-501017 corresponds to WO 95/02895, the content of which is incorporated by reference in its entirety into this application. Japanese Patent Application Pre-examination Publication No. JP-A-06-224168 discloses an apparatus for removing the photoresist by using an ozone gas. In addition, Japanese Patent Application Pre-examination Publication No. JP-A-01-189921 proposes an apparatus for removing the photoresist by using the ozone-dissolved SPM.
Referring to FIG. 5, there is illustrated an example of a prior art photoresist removing apparatus, which is a sheet-feed type wet treating machine so configured to treat wafers one after one.
As shown in FIG. 5, this photoresist removing apparatus comprises a rotating stage 2 for supporting a semiconductor wafer 1 thereon, a chamber 5 accommodating the stage 2 therein, a discharge nozzle 3 for discharging an ozone-dissolved water to a photoresist formed on the semiconductor wafer 1, and an ozone-dissolved water generator 4 discharging the ozone-dissolved water to the discharge nozzle 3.
This photoresist removing apparatus is used as follows:
First, after the semiconductor wafer 1 is vacuum-sucked to the stage 2, the semiconductor wafer 1 is rotated. In this condition, the ozone-dissolved water is discharged together with a deionized water (abbreviated to xe2x80x9cDIWxe2x80x9d hereinafter) from the discharge nozzle 3 onto the semiconductor wafer 1. The photoresist deposited on the semiconductor wafer 1 is removed by the ozone-dissolved water thus discharged.
However, the following problems have been encountered in the prior art method for removing the photoresist by using the ozone-dissolved water.
The concentration of the ozone dissolved in the DIW is inversely proportional to a DIW temperature. Namely, the higher the DIW temperature becomes, the lower the concentration of the ozone dissoluble to the DIW becomes.
Referring to FIG. 6, there is shown a graph illustrating the relation between the DIW temperature and the concentration of dissoluble ozone. For example, when the DIW temperature is at 5 degrees Celsius, about 120 ppm of ozone is dissoluble. When the DIW temperature is at 25 degrees Celsius, only about 65 ppm of ozone is dissoluble.
An etching rate of the photoresist by the ozone-dissolved water is in proportion to the concentration of the ozone in the DIW and also in proportion to the temperature of the ozone-dissolved water.
Accordingly, it is ideally preferred that the concentration of ozone in the ozone-dissolved water is high and the temperature of the ozone-dissolved water is also high. However, since the temperature of the ozone-dissolved water and the concentration of ozone in the ozone-dissolved water are in inverse proportion to each other as mentioned above, even if the ozone-dissolved water having a high concentration of ozone is prepared at a low water temperature, when the water temperature is elevated later, the ozone in the ozone-dissolved water is decomposed, with the result that when the ozone-dissolved water is actually discharged to the photoresist, the ozone-dissolved water has already become an ozone-dissolved water having only a low concentration of ozone.
As mentioned above, in the prior art photoresist removing method, it is not possible to remove the photoresist by using a high concentration, high temperature, ozone-dissolved water, with the result that the photoresist removing was not necessarily effectively carried out.
Accordingly, it is an object of the present invention to provide a photoresist removing method and apparatus, which have overcome the above mentioned problem of the prior art photoresist removing method.
Another object of the present invention is to provide a photoresist removing method and apparatus, capable of making it possible to remove the photoresist by using a high concentration and high temperature ozone-dissolved water.
The above and other objects of the present invention are achieved in accordance with the present invention by a method for removing a photoresist on a semiconductor wafer by using an ozone-dissolved water, the method comprising a first step of elevating the temperature of the semiconductor wafer, and a second step of discharging the ozone-dissolved water onto the semiconductor wafer when the temperature of the semiconductor wafer reaches a predetermined temperature.
With the above mentioned photoresist removing method, the ozone-dissolved water is maintained at a low temperature until just before the ozone-dissolved water is discharged onto the semiconductor wafer. In other words, the ozone-dissolved water is maintained to have a high concentration of ozone until just before the ozone-dissolved water is discharged onto the semiconductor wafer. If the ozone-dissolved water having the high concentration of ozone is discharged onto the semiconductor wafer, since the temperature of the semiconductor wafer has been previously elevated to the predetermined temperature which is higher than that of the ozone-dissolved water thus discharged, the temperature of the ozone-dissolved water elevates upon the instant. With elevation of the temperature of the ozone-dissolved water, the decomposing reaction of the ozone occurs at a surface of the semiconductor wafer. With this decomposition of the ozone, a chemical reaction between the ozone and the photoresist is expedited. As a result, the etching rate of the photoresist is increased, so that the time required to remove the photoresist can be shortened.
According to another aspect of the present invention, there is provided a method for removing a photoresist on a semiconductor wafer by using an ozone-dissolved water, the method comprising a first step of elevating the temperature of the semiconductor wafer, a second step of discharging the ozone-dissolved water onto the semiconductor wafer when the temperature of the semiconductor wafer reaches a predetermined temperature, a third step of carrying out a rinse treatment for the semiconductor wafer, and a fourth step of drying the semiconductor wafer.
With this arrangement, the removing rate of the photoresist can be increased by discharging a low temperature, high concentration, ozone-dissolved water, similarly to the method in accordance with the first aspect of the present invention.
In one embodiment, in the second step, the semiconductor wafer is rotated around a center of the semiconductor wafer, and the ozone-dissolved water is discharged onto the rotating semiconductor wafer.
By rotating the semiconductor wafer, it is possible to discharge uniformly the ozone-dissolved water over the semiconductor wafer.
In a preferred embodiment, in the second step, during a period in which the ozone-dissolved water is discharged onto the semiconductor wafer, the semiconductor wafer continues to be heated.
By continuously heating the semiconductor wafer, it is possible to maintain the semiconductor wafer at the predetermined temperature, with the result that it is possible to continue the decomposing reaction of the ozone occurring at the surface of the semiconductor wafer. Therefore, it is possible to avoid the drop of the removing rate of the photoresist.
Preferably, the predetermined temperature is maintained at a temperature of not less than 100 degrees Celsius.
According to a third aspect of the present invention, there is provided an apparatus for removing a photoresist on a semiconductor wafer, the apparatus comprising a heater for heating the semiconductor wafer, an ozone-dissolved water generator for generating an ozone-dissolved water, and a discharge means for discharging the ozone-dissolved water generated by the ozone-dissolved water generator, onto the semiconductor wafer.
With the photoresist removing apparatus mentioned above, it is possible to discharge the ozone-dissolved water onto a photoresist formed on the semiconductor wafer by the discharge means after the semiconductor wafer is heated by the heater. Therefore, the ozone-dissolved water can be maintained at a low temperature until just before the ozone-dissolved water is discharged onto the semiconductor wafer. In other words, the ozone-dissolved water can be maintained to have a high concentration of ozone until just before the ozone-dissolved water is discharged onto the semiconductor wafer. If the ozone-dissolved water having the high concentration of ozone is discharged onto the semiconductor wafer, since the temperature of the semiconductor wafer has been previously elevated to the predetermined temperature which is higher than that of the ozone-dissolved water thus discharged, the temperature of the ozone-dissolved water elevates upon the instant. With elevation of the temperature of the ozone-dissolved water, the decomposing reaction of the ozone occurs at a surface of the semiconductor wafer. With this decomposition of the ozone, a chemical reaction between the ozone and the photoresist is expedited. As a result, the etching rate of the photoresist is increased, so that the time required to remove the photoresist can be shortened.
Preferably, the photoresist removing apparatus further includes a temperature sensor for sensing the temperature of the semiconductor wafer and a controller for controlling the heater on the basis of the temperature of the semiconductor wafer sensed by the temperature sensor.
By monitoring the temperature of the semiconductor wafer by the temperature sensor, it is possible to freely control the heater by action of the controller, with the result that the temperature of the semiconductor wafer can be maintained at a desired temperature.
For example, the heater can be constituted of an infrared lamp for irradiating infrared rays to the semiconductor wafer.
Furthermore, the photoresist removing apparatus includes a stage on which the semiconductor wafer is placed, and the heater can be incorporated in the inside of the stage.
If the heater is incorporated in the inside of the stage for supporting the semiconductor wafer thereon, it is possible to effectively heat the semiconductor wafer